Simple differences between mixtures and compounds
3 marks · EasyA student has the following substances:
| Substance | Description |
|---|---|
| Hydrogen | Colourless gas, only one kind of atom |
| Calcium oxide | Solid, contains calcium and oxygen chemically combined |
| Air | Mixture of different gases |
Which substance is an element? Explain your answer.
Which substance is a compound? State its chemical formula.
Why is air described as a mixture?
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Show answer
(a) Hydrogen is an element because it consists of only one type of atom.
(b) Calcium oxide is a compound; its formula is CaO.
(c) Air is a mixture because it contains different gases not chemically combined.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly identifies hydrogen as an element and explains why.
B2 (b) · 1 mark · Identifies calcium oxide as a compound and gives correct formula (CaO).
B3 (c) · 1 mark · Explains that air is a mixture as it contains different gases not chemically combined.
Worked solution
a) Hydrogen is an element because it contains only one type of atom.
b) Calcium oxide is a compound; its chemical formula is CaO.
c) Air is a mixture because it is made of different gases that are not chemically combined.